20th March 2019

NEW ANTI-CORROSION TECHNOLOGY

Researchers at Johannes Gutenberg University Mainz (JGU), in Mainz, Germany, have developed a method to hinder hazardous seawater fouling and is reportedly effective, affordable and easy on the environment. Fouling can occur from the growth of bacteria, algae or mollusks in harbor facilities, on boat hulls and aquaculture netting. The resultant damage and consequential costs are estimated at $200-billion annually in the shipping industry alone.

Protective coatings applied to vessels usually contain copper-based biocides. These have the disadvantage that they harm the environment while resistance to them can also develop. In order to find an alternative, the research team under Professor Wolfgang Tremel decided to simulate a defense mechanism employed by algae, and established that cerium dioxide nanoparticles can effectively prevent fouling. This discovery could contribute to the development of new protective coatings that are much less environmentally harmful than the hull coatings in use now.

Marine algae use secondary metabolic products in order to have a form of chemical defense against micro-organisms and predators. These halogenated secondary metabolites specifically prevent bacterial biofilms, other algae, and even barnacles from becoming attached to and developing on larger formations of algae, sponges and other creatures.

Halogenated compounds produced by the red seaweed Delisea pulchra, for instance, inhibit bacterial fouling but are neither toxic nor growth retarding. The Mainz-based team of chemists used nanoparticles of cerium dioxide to mimic this natural defense process.

"Field tests have shown that cerium dioxide is an ecologically acceptable alternative to cuprite, a substance that is used as a biocide together with copper thiocyanate and copper pyridine at concentrations of up to 50 percent in anti-fouling coatings," explained Professor Wolfgang Tremel of JGU’s Institute of Inorganic Chemistry and Analytical Chemistry. But such copper compounds are toxic and accumulate in the environment. This is why some countries, such as Canada and Denmark, have imposed strict limitations on the use of copper-based anti-fouling coatings.

"All modern catalytic converters in vehicles use cerium dioxide. It is non-toxic and chemically extremely stable," added Karoline Herget, who wrote her doctoral thesis on the project. She says cerium dioxide is a practical and cost-effective alternative to conventional biocides.

Cerium dioxide is an oxide of the rare earth element cerium and a byproduct of the process of extraction of rare earth metals. Despite belonging to the family of rare earth elements, cerium itself is not particularly scarce. Its cost is thus comparable with that of cuprite (copper(I) oxide), although it is effective in far lower quantities.

"What we have here," Herget continued, "is an environmentally compatible component of a new generation of anti-fouling coatings that simulate the natural defense systems employed by marine organisms. What is important is that it is effective not only under laboratory conditions but also when actually used in the aquatic environment."

Steel panels with cerium oxide coatings can be exposed to seawater for weeks on end without becoming covered by bacteria, algae, mollusks or barnacles. Reference samples with conventional water-based coatings develop massive fouling over the same time period.

Biofilms exist in many places: drinking water pipes and clarification plants, in ground water, water filtration and cooling systems, on practically all surfaces such as food packaging, door handles, push buttons, keyboards, and other elements made of plastic. In medicine, they also develop in catheter tubes.

The research project was undertaken in cooperation with BASF, and the results have been published in the journal Advanced Materials.

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